Volume-cycled respirators which have been used in the past and those which are presently in use are cumbersome in nature. Most of them make use of piston-bellows assemblies to deliver the tidal volumes of breathing gas to the patient. Conventional respirators are fairly complex and further employ a variety of elements including snap valves, springs, solenoid valves, magnets, gear boxes, ratchets, mechanical linkages, pulleys, photocells, electronic circuitry, and other components to provide a number of functions. The complexity and hybrid nature of these systems results in large, massive and expensive respirator units which are somewhat fragile and susceptible to mechanical failure. Basically, most of them have numerous moving parts which makes the apparatus more complex to operate and maintain.
The present invention relates to a fluidic volume-cycled respirator circuit which is relatively simple in its construction; contains few, if any, moving parts; is highly efficient; and is convenient to use and transport. The respirator herein basically comprises an input valve, a flowmeter and a controller.
In order to better understand the present invention, one should understand the prior art teachings in the field of respirators.
Respirators comprising (1) a control circuit which is responsive to a (2) sensor are taught by Durkan and Durkan et al. in U.S. Pat. Nos. 4,462,398; 4,506,666; 4,519,387 and 4,570,631. The control circuits described therein operate an input valve. The sensor picks up the negative pressure sensed from the patient using the respirator. The sensor then, in accordance with its sensing of the negative pressure, instructs the control circuit to operate the input valve in response to the patients' needs. The control circuit may also operate the valve if no negative pressure is sensed within a predetermined time period. Hence, the respirator disclosed operates based on the change in pressure from the patient and based on a predetermined time set to control the supply valve. Note that the patents may additionally make use of a conventional flowmeter. The sensor taught may be fluidic; and the valve is electrically controlled by the control circuit. The patents further teach generally that other fluidic elements can be used in their respirator circuit.
The Durkan and Durkan et al. references discussed above are very elaborate breathing devices. They make use of both fluidics and electronics in their sensor means and control circuits. The fluidic devices are fluidic amplifiers. Based on the description of the Durkan patients above it may appear that these references teach our invention. This is not so because our invention is able to provide the same service as Durkan but using a more reliable and compact system. The respirator herein is not as complex as those taught by these patent references. Moreover, our invention makes use of fluidic oscillators, as opposed to fluidic amplifiers. The use of one is not an obvious sustitution or modification for the use of the other.
U.S. Pat. No. 4,461,293, issued to Chen, teaches a breathing apparatus similar to that taught by Durkan. In this teaching, a control circuit is responsive to a sensor which operates a valve to supply breathing gas to a patient. This system, however, is a more complex system than that of the present invention. Moreover, unlike the teaching in Chen, the present invention makes use of a fluidic oscillator as the flowmeter as opposed to a fluidic amplifier.
Perkins, U.S. Pat. No. 4,705,034, teaches a respiratory apparatus which may use fluidic sensors--note, column 4, lines 49-65. Sensors of this type are able to detect the onset of inhalation and the volume metering of the breathing gas. The respirator taught by Perkins is a demand system which requires the use of an electrical solenoid to activate the input valve. In addition, the metering system therein has many moving parts. This system makes use of a piston which our invention avoids. Perkins teaches a much more elaborate system than that of the present invention.
U.S. Pat. No. 4,054,133, issued to Myers, teaches a respirator apparatus that comprises a control means which is responsive to inhalation, pause and exhalation of a patient. Its response regulates the flow of oxygen from a supply chamber to said patient. Reduced pressure activates an input valve to only allow oxygen flow during inhalation. This breathing apparatus makes use of a diaphragm to sense the pressure differential due to the patient's breathing. In addition, nowhere does Myers indicate any use of fluidics in his breathing device.
U.S. Pat. No. 4,381,002, issued to Mon, one of the inventors herein, teaches a respirator which comprises a valve, a fluidic control system which senses inspiration and exhalation, and an oxygen source. This patent, however, does not mention the use of a fluidic flowmeter. Moreover, the Mon respirator makes use of a diaphragm and a fluidic amplifier controller, neither of which is within the scope of the present invention.
U.S. Pat. No. 4,278,110, issued to Price et al., claims a respirator which utilizes a fluidic valve, a flowmeter, a flow controller which senses expiration and inspiration, and an oxygen source. The oxygen is supplied on a demand basis only. A fluidic oscillator is not use in Price et al. Moreover, our invention does not require the use of a fluidic valve.
U.S. Pat. No. 3,896,800 teaches that the use of fluidic and electronic respirator control devices is well known. The apparatus taught, however, requires the use of a diaphragm.
U.S. Pat. No. 4,019,382, issued to El-Gammal, sets forth the general teaching of the well-known use of a fluidic flowmeter which measures respiratory functions. Note that the flowmeter is for use with cumbersome breathing apparatus. The breathing apparatus does not teach the respirator circuit claimed herein.
U.S. Pat. Nos. 4,120,300; 4,289,126 and 4,414,982 are recited to give the reader more background on the general teachings of the use of fluidics in the respirator art areas.
The use of fluidics in respirators is not a novel one. Note, "Respiratory Care Applications for Fluidics," Respiratory Therapy, pp. 29-32 (1973).
As one may note from the teachings in the prior art with regard to respirators, the individual concepts of using fluidics, control devices, sensors, etc. are not novel. More particularly, the use of fluidic control systems and fluidic sensors are further well known. However, the combination of these concepts are neither taught nor suggested in the prior respirator art.
It is the combination of these general components which result in the hand-held respirator of the present invention.